It is preferable to use fluid flow control devices rather than using conventional mechanical type controls relying on an arrangement of levers and cables, since fluid flow devices provide easier and smoother control. In addition, in the event that a source of reduced pressure breaks down or stops, the moving members may be automatically returned to a privileged or safety position by return springs acting on the displacement actuators. However, fluid flow control devices have only been used heretofore for displacing a single flap at a time, or in the limit, two flaps when said flaps are displacable along trajectories which do not cross each other.
However, installations for heating and ventilating or for air conditioning vehicles do exist which comprise a variety of flaps that are rotatably mounted about parallel axes and that are actuated by a single control device in order to be displaced through predetermined positions, which displacements may be synchronized or not, depending on circumstances, with the flaps being generally intended to mix and distribute flows of hot air and cold air passing through the installation. Since the flaps are relatively close to one another, their trajectories may intersect. It is thus possible, in such an installation, for it to be impossible to move two flaps simultaneously since one of the flaps may need to be moved before the other flap is moved in order to prevent said flaps from abutting against each other and jamming or otherwise interfering with the intended motions.
The relatively complex problems which are encountered when controlling the flaps in an installation of this type have been solved heretofore by mechanical means including cam arrangements, which further increase the force which the user must apply to the control means, at least in some positions thereof which correspond to awkward functions in the installation, and this can even lead to the flaps becoming jammed in some conditions of vehicle use, for example when the vehicle is travelling at very high speed and the flaps are in positions for closing outlet orifices from the housings in which they are located.
Preferred implementations of the present invention provide fluid flow apparatus for controlling moving members, such as the flaps of an installation for heating and ventilating or for air conditioning a motor vehicle, which apparatus avoids the drawbacks of mechanical apparatus for performing the same purpose and is applicable to any multi-flap installation regardless of whether the flap trajectories intersect or not.